The present invention relates to a magnetic recording and reproducing method in which a signal magnetically recorded on a magnetic recording medium is reproduced with an MR head, and a magnetic recording medium employed for the magnetic recording and reproducing method.
In particular, the present invention relates to a magnetic recording and reproducing method in which a signal magnetically recorded on a magnetic recording medium for high-density recording comprising a substantially nonmagnetic lower layer and a magnetic layer comprising a hexagonal ferrite ferromagnetic powder and a binder in this order is reproduced with an MR head, and a magnetic recording medium employed for the method.
In the field of magnetic recording disks, 2 MB MF-2HD floppy disks employing Co-modified iron oxide have been mounted normally in personal computers. However, today, with the rapid increase in the volume of data handled, the capacity of such disks is inadequate and there is a need for the development of high-capacity floppy disks.
In response to the demand for high-capacity floppy disks, a disk-shaped magnetic recording medium comprised of a thin magnetic layer and a functional nonmagnetic layer has recently been proposed, and floppy disks in the 100 MB class have been developed. Examples of disk-shaped magnetic recording media having such characteristics are those described in Japanese Unexamined Patent Publication (KOKAI) Heisei Nos. 5-109061 and 5-290354. That is, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-109061 discloses a configuration having a magnetic layer with a coercive force Hc equal to or higher than 111 kA/m (1,400 Oe) and a thickness equal to or less than 0.5 xcexcm, and a nonmagnetic layer comprising electrically conductive particles. Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-290354 discloses a configuration having a magnetic layer equal to or less than 0.5 xcexcm in thickness, with the thickness variation in the magnetic layer being within xc2x115 percent, and the surface electrical resistivity being prescribed.
In the field of magnetic recording tapes, with the widespread popularity of office computers such as minicomputers, personal computers, and work stations in recent years, a large amount of research has been conducted into magnetic recording tapes (so-called xe2x80x9cback-up tapesxe2x80x9d) used to record computer data as an external memory medium. In the practical implementation of magnetic recording tapes for such applications, particularly as the size of computers has decreased and information processing capability has increased, there had been strong demand for an increase in recording capacity to achieve high-capacity recording and size reduction. Further, there has been further demands than in the past for reliability for the use and data storage under the wide environmental condition (in particular, under the condition in which a temperature and a humidity change intensely) due to broaden an environment in which magnetic recording tapes are employed, and for reliability for performance such as stable data-recording and readout in multiple running by repeated use at high speed.
In the past, the magnetic recording tapes employed in digital signal recording systems were determined by system, with magnetic recording tapes corresponding to model DLT; models 3480, 3490, and 3590; model QIC; model D8; and model DDS being known. Further, irrespective of the system, the magnetic recording tape employed comprises a magnetic layer comprising a ferromagnetic powder and a binder with a single-layer structure of comparatively high thickness of 2.0 to 3.0 xcexcm on one side of a nonmagnetic support, with a backcoat layer preventing uneven winding and ensuring good running durability being provided on the opposite surface from the magnetic layer. However, magnetic layers of the comparatively thick single-layer structure as mentioned above normally has a drawback in the form of thickness loss causing noise reduction.
To achieve improvement in reproduction output reduction caused by thickness loss in such magnetic layers, it is known that making the magnetic layer thin is effective. For example, Japanese Unexamined Patent Publication (KOKAI) Heisei No. 5-182178 discloses a magnetic recording medium in which a lower nonmagnetic layer comprised of an inorganic powder dispersed in a binder is applied on a nonmagnetic support and an upper magnetic layer of a thickness equal to or less than 1.0 xcexcm in which a ferromagnetic powder is dispersed in a binder is provided thereover while said nonmagnetic layer is still wet.
However, with the rapid development of high-capacity and high-density magnetic recording disks and magnetic recording tapes, it has become difficult to achieve satisfactory characteristics even if using techniques such as those set forth above. In particular, when increasing the linear recording density and recording at high frequency to achieve both high capacity and a high data transfer rate, it is difficult to achieve adequate recording and reproduction characteristics in conventional media.
Thus, the present invention was devised in light of the above-described problems. It is an object of the present invention to provide a method of magnetic recording and reproducing capable of permitting high density recording on magnetic recording media even under the condition of high data transfer rates and yielding adequate recording and reproduction characteristics when a magnetoresistive head (referred to as an xe2x80x9cMR headxe2x80x9d hereinafter) is used in reproduction. A further object of the present invention is to provide a magnetic recording medium characterized by being used in this magnetic recording and reproducing method.
The present inventors conducted extensive research into methods of obtaining magnetic recording media having good electromagnetic characteristics, and in particular, extremely good electromagnetic characteristics when a signal magnetically recorded at high frequency was reproduced with an MR head. As a result, they discovered a method capable of yielding good high-density characteristics, unprecedented in the art, by reproducing with an MR head a signal having a prescribed frequency and magnetically recorded on a magnetic recording medium satisfying prescribed conditions; the present invention was devised on this basis.